Radio pulse position indicating system



l. woLFF ET AL 2,403,626

RADIO PULSE POSITION INDICATING SYSTEM Filed Nov. 29, 1941 July 9, 1946.

SPL/T751? 1640/0 PULSE IBEGE/Vf nventors Cttomeg memes July e, lme

UNITED STATES PATENT orsi-CE m10 ILSE l:NDICIING IrvlngWolflandBliphSJlolm Baddcncld N. I., to Radio corporation of America, a corporation of lDelaware 'application November ze. 194i. No. 420,944

l l Claims. This invention relates to improvements in radio pulse position indicating systems and particularly to a radio puise position indicating system in which pulse signals radiated from a plurality of synchronized pulse transmitters j timed with respect to each other so that the differences in pulse propagation timesindicate the position of the receiver. A system for indicating the propagation times of an aircraft receiver (located at an unknown point) and relayed from two xedly positioned relay transmitters back to a receiver on the aircraft, has been tion Serial No. Stuart Seeley. An device is described position by? measuring pulses radiated from 329,434, med April 13, 1940, vby improvement of the Seeley in copending application Serial No. 384,323, filed March 20. 1941, by Irving Woll! for improvements in Position ilnders.- The Wolff improvement describes a decade type of cathoderay timer. v

In the Seeley device, a moving vehicle. such as a plane, is equipped withv a pulse transmitter and receiving apparatus includinga cathode ray indicator. Pulses t ytteti from the plane are received at two ground stations at known locations. Each ground station coin-prises a radio relay which re-radiates the pulses at a slightly different frequency. The re-radiated pulses are received on the plane and compared on the cathode ray indicator to provideindications of the distance and position of the plane with respect to the known locations of the ground relay stations. J

The Wolff device describes a system similar to that of the Seeley device with the addition of a decade vernier type of cathode ray indicator for providing accurate indications, of the distances of the relay stations from the plane. The Vernier scales are produced by utilizing a plurality of cathode ray indicators in which the respective cathode ray beams are rotated at relative speeds of 1:10:100.

While the Seeley device and the Wolif improvement thereof are accurate and practical, there may be two objections: First, in time of war the signals from aircraft transmitters may be received by the enemy who will be able to locate the signal source by conventional radiogoniometric methods and thereafter destroy the air-fv craft before it can reach its objective; and second, the described system is designed to tion a single aircraft or other vehicle and it is are received and I described in an allowed applicav lil 2u of the invention.

.25 though anymeans may to the accompanying (ci. aso-1),v

' different courses coulduse the same relays'withn out confusion.

One of the objects of the present invention is to provide improved means for indicating position 'as a function of the differences in times of reception of a plurality of pulses radiated simultaneously or in predetermined time relation from "a plurality of at predetermined points. Another object is to provide an improved positionA indicating system in vwhich the transmitted signals are pulses of radio vfrequency energy radiated in synchronism from points of known location. Another object is to provide a 'decade type off-pulse timer in whichone group of theincoming puissto be timed is used t'o synchronize the timer.

The invention will be' described by referring drawing in which the schematic' diagram represents Referring to the figure of the drawing, radio transmitters are located at known positions A, B and C. The erably connected by a synchronizing line, al-

be used to control the radiation of pulses D, D' and D" in predetermined time relation. The pulses are sharply denned,and are radiated at high and, ify desired, diilerent, carrier frequencies and at relatively low pulse frequenciesfor long range operation.

40 puise D" a5 receiver,

- E to'A or from E By way of example, the carrier frequency may be-500 megacycles and 335/3 -pulses per second maybe radiated. These pulses are received on an aircraft E at the same time if the aircraft indicated generally as F is equally distant from the three transmitters. Ii the receiver F is equally distant from A and B but at some other distance from C, the pulses D and D' will reach E at the same time. while the will reach E at an earlier or later time dependent upon whether the distance from E to C is less than or more than the distance from 'nave been shown between the transmitter and 445 receiver, it should be kunderstood that the pulse 1 rate is designed for the maximum range and for the prevention of' pulse repetition within the range, which would be confusing.` Actuallyv only f a single pulse would appear. between any of the transmitters and the receiver at any instant, if the receiver is within the maximum v which the systemisdesigned.

The transmitters are preferably not symmetricallylocated in the same'straight line, be-

not apparent how a large number of vehicles on es cause such location would result in amradio pulse transmitters located one embodiment transmitters are prefto B. While several pulses' range for The output of the third frequency divider 43 is applied to the balanced modulator and rectifier 3. The output of the balanced modulator and rectifier is applied to an automatic frequency control device 45. The output of the frequency control device 45 is applied to the first oscillator to syiiclironize,gthe localj'foscilllatic with the inpropagation times which willexist at any predetermined location so that the aircraft opere ator may simply ily a course which tends to bring the several differences in pulse propagation times to the predetermined values. A.

For example, if the distances AE=300` kilometers; BE=310 kilometers; and CE=295 kilometers, the several propagation times in microseconds will equal the velocity of light (which is 300,000 kilometers per second) divided into the distance. Thus the pulse propagation time from A to E will equal .001 second or 1000 microseconds, B to E pulse propagation time will equal 1033.3 microseconds; and C to E pulse propagation time will equal 983.3 microseconds.

Therefore, lthe dilerences in pulse propagation times will be as follows: BE minus AE will be 33.3` microseconds; BE minus CEV will be 50 microseconds; and AE minus CE will be 16.7 microseconds. With the irregular positioning of the transmitters there is only one map position which will correspond to these differences in time. An aircraft pilot can ilythe aircraft until these time differences.v are indicated on the aircraft pulse receiver and then the aircraft will -be at the specified or predetermined position.

One suitable aircraft receiver is indicated in the figure of the drawing. A radio pulse receiver `I is connected to a balanced modulator and rectifier 3 which may be of the type described in U. S. Patent 2,234,587 having any conventional rectifier connected in its output circuit, and to the radial defiecting electrodes 5, 1, 9 of three cathode ray indicators II, I3, I5. The function of the balanced modulator will be described later. The cathode ray indicators form decade timing indicators which are connected as follows: A- stabilized oscillator II, preferably arranged within a temperature controlled compartment I9, is connected through a phase shifter 2l to a phase splitter 23. The two phase output of the phase splitter is applied to the defiecting elements 25 of the first cathode ray tube I I to produce a rotating field. The current from the stabilized oscillator Il is next applied to a frequency divider 2l to lower the frequency tenfold. The currents of reduced frequency are applied through a second phase shifter 29 and a second phase splitter 3l to the defiecting elements 33 of the second cathode' ray tube I-3 to produce a rotating field of one tenth the angular velocity of the eld in the first tube. The output of the rst frequency divider 21 is also applied to a second frequency divider 35 which again divides the frequency by ten. The output of the second frequency divider 35 is applied through a third phase shifter 31 and a third phase splitter 39 to the deiiecting elements 4I of the third cathode ray tube I5 to produce a rotating field having an angular velocity equal to one tenth of the angular velocity of the field in the second tube.

The output of Vthe second frequency divider 35 is applied to a third frequency divider` 43,

.which reduces the frequency to the pulse rate..75

llfhe mode of operation is as follows: 'I'he local oscillator may be operated at kilocyclesper second. A'Iv'hecurrents from the local oscillator I1 are applied through theI phase shifter 2| 'which permits the first received pulse to be phasedto correspond to the zero of the cathode ray tube scale 41:" The suitably phased currents are split into currents of quadrature phase and are applied to the deflecting elements 25 to produce a rotating field. The rotating field causesV the cathode ray to rotateat 100,000 revolutions per second. The oscillator currents of a frequency of 100 kc. are divided to establish currents of a frequency-,of l0 kc. 10 kc. are phasedby, the second phase shifter 29 so that the zero of the second cathode ray tube scale 49 may bemade to correspond with the first received pulse. The currents of 10 kc. are split into two phase currents, which are applied to the deecting elements 33 of the second cathode ray tube to produce a rotating field. Thisiield rotates the ray of the second cathode ray tube 10,000 times per second. The `local vcurrents are further divided in frequency and,

y WfIjhe yincoming pulses are applied tothe several radial deflecting electrodes 5, 'I and 9 to deflect radially thel rotating cathode rays. Since the rays are rotating relatively slowly in the third tube I5 only large differences in the times of arrival of the pulses from the three transmitters will .be indicated. For example, a complete rotation of the ray corresponds to 1000 microseconds. The second tube I3 has a ray which rotates ten times as fast so that one complete rotation will correspond to 100 microseconds. The first tube, with its ray rotating one hundred times faster than the ray of the third tube, will have a scale in which one complete rotation corresponds to l0 microseconds. Since the scale 4l may be divided into 100 parts, it follows that a time difference of .1 microsecond may be indicated without diiliculty. The pulses travel 300 meters in one microsecond, therefore 30 meters in .1 microsecond, so that distances may be readily determined to within 30 meters or better.

In order that the local oscillator I 'I may be synchronized with the incoming pulses, the local currents are frequency divided until a current -of the pulse frequency is derived. For example,

331/3 cycles per second, which corresponds to a maximum range of nearly 10,000 kilometers, has been chosen as the pulse frequency. The incoming pulses are detected and are applied at the pulse rate of 33%; C. P. S. to the balanced modulator 3, to which the alternating current obtained by frequency division at the rate of 331/3 C. P. S. are also applied.- -As long as'the two currents are of identical phase or frequency, no output is obtained fromv the balanced modulator. If the frequency or phase of the local oscillator varies, a. current will appear in the output of the balanced modulator. The output current, if not already rectified in the balanced modulator, may be rectified and applied through The currents of i amm.

or decrease the frequency ofthe local oscillator I1. The local oscillator is thus locked-in with the transmitter pulse frequency. The locking-in may be aifected by the pulses arriving at different times from the several transmitters. In this event the carrier of one of the transmitters is made slightly diiferent. The pulse receiver, which is preferably a superheterodyne. is made v with an intermediate frequency ampliner responsive to both carriers, which are then sep-` arated by filtering the currents of thecarrier to be applied to the balanced modulator. v Thus filtered only the pulses of the selected carrier are used to lock-in the local oscillator. It should be understood that the filter 53 may include tuned intermediate frequency. ampliilerjstages andadetector. v

In the system described no means are provided for distinguishing the pulses from the several transmitters. It is not essential that the .pulses be distinguished because they aircraft carrying the receiver may be flown along a course and, by l observing whether the pulses are approaching each other or receding from each other, the operator may determine i-f-the course is bringing the craft toward or away from the several. transmitters. If more precise sired, a radio goniometer may be used to indicate the bearing of any one of the transmitters. if their carriers are distinguishable. It should be understood that three separate receivers may be used to receive three different carriers thereby making continuous identiilcation practical. In place of three separate receivers a single receiver may be successively tuned to the several carriers. Another method of distinguishing the transmitted ypulses is described in the copending applications hereinafter cited.

Inasmuch as the slowest ray rotates ten times for each pulse and the fastest a thousand times for each pulse, it will be diillcult to observe thel pulses if the rotating ray is continuously applied to the fluorescent screen of the cathode ray tubes. One method of avoiding the diiliculty is to mask the rotating ray at all times except during the radial deflection. y by optical or electrical means. If electrical means are used, the ray is biased of! for all but one or two rotations which include the received pulse. Suitable means for blanking manually or automatically are disclosed in copending applications Serial No. 420,919, nled November 29, 1941, by John P. Smith, and Serial No. 420,928, filed November 29, 1941, by Ralph S. Holmes and John P. Smith.

We claim as our invention:

1. A radio pulse position indicating system in.- cluding means for radiating synchronously discrete pulses of radio energy from a plurality of predetermined locations, remotely located receiving means including means for receiving said pulses, a source of dicator, means-connecting said source to said indicator for applying said oscillations to drive said indicator at a, substantially constant rate, means connecting said receiver andlocal source for synchronizing said local oscillations and said pulses, and means for applying said received pulses to said indicator to indicate the differences in times of said pulse reception thereby to indicate the distance of said receiver .from each of said predetermined locations.

2. A radio pulse position indicating cluding means for radiating predetermined relaf system inpulses,

.reception thereby to tively'nmedrdiscre pulses located receiving ceiving said pulses, a source of a timing indicator, means connecting said source to said indicator for applying said oscillations` to drive said indicator at a-substantiallyconstant angular rate, means connecting said receiver and `localsource for synchronizingl vsaid f y said pulses, and means vfor i applying said ,-received'pulses to saidv indicator local oscillationsI and to indicate the diilerences in times of said pulse indicate the distance of said receiver from each of tions. w l l 3. .A radio pulse position. indicating system invcluding means for radiating pulses of'radio energy from v`a plurality of "predetermined locations,

means for synchronizing the radiationv vofsaid pulses so'that all pulses are radiated in prede,- termined phase relation, remotely:located receiv.

ing means including. means indicator, a source of oscillations, means connect?- information is de ing said source to each of said indicators, for I driving said indicators at different substantially constant rates, and means connecting said receiving means to said indicators for applyingreceived pulses to. said indicators to denote their relative times of reception whereby the distance i of said receiver fromv each 'of said locations may .be indicated as functions of said relative times.

4. A radio pulse rposition indicating 4system in cluding'means for radiating pulses of radio energyl from a plurality of predetermined locations, means for synchronizing the radiation of said pulses so that all pulses `are radiated in a predetermined phase relation, remotely located receiv- Y ing means including means for receiving said pulses, a timing indicator,

for driving said indicator-ata substantially con--V stant rate, means connecting said receiving means-to said indicator for applying received of radio energy local oscillations, a timing in-v predetermined time relation, remotely located receiving means including means for receiving said pulses, a timing indicator, a source of oscillations,

means connecting said source to said indicator for driving said indicator at a substantially constant rate, means connecting said receiving means to said indicator for applying received pulses to said indicator to denote their relative times of `reception whereby the distance of said receiver from each' of said locations may be indicated as functionsof said relative times, and means conceiving lations ne'cting said source of oscillations and said re,- means for synchronizing said local oscilwith one of said plurality of distinguishable pulse radiations.

6. A pulse receiver and indicator for a position .indicating system including means for receiving Y of cathode ray tubes. a

substantially consaid pulses. aplurality source of local oscillations of of radio energy from l apluralltyfo'f predetermined locations. remotely means including means for ref local oscillatio said predetermined loca,-

for receivingl said a main timing indicator, a vernier timing' asource of oscillations, meansconnecting said source to said indicator.

stant frequency, means vconnecting-said source to one or said tubes :or appyling said oscillationsto lower frequency, means connecting said pulse reio ceiving means to said-tubes for applying said received pulses to produce visual indications on said tubes to indicate differences in the times of re-l ception of said pulses, and means connecting said receiving means and said source for synchronizing said local oscillations with the received pulses.

7. A pulse receiverand indicator for a radio positioning system including a pulse receiver responsive to position indicating pulses, a source of'- local oscillations of substantially constant frequency, means connecting said receiver to said source for applying the received pulses to control said substantially constant frequency, a plurality of cathode ray tubes, means connecting said source to onelof said tubes for, applying said oscillations of constant frequency to rotate its ray at said constant frequency, means for dividing said oscillations of constant frequency to produce.

oscillations of frequencies of one tenth-V and one hundredth of said constant frequency, means connecting said frequencyv dividing means to a second `of said tubes for applying said oscillations of one tenth frequency to rotate the ray of said second tube, means connecting said frequency dividing means to a third of said tubes for applying said oscillations of one hundredth frequency to rotate the ray of said vthird tube, and means connecting said receiver to said tubes for applying pulses derived from the output of said receiver to deflect radially the rays of said cathode ray tubes and hence to indicate the relative times of reception of said pulses.`

8. A pulse receiver and indicator according to `means Afor synchronizing claim 7 including means connecting said receiver and said source for' phasing the oscillationsl appliedto rotate the rays of said cathode ray tubes so that said rotating rays may be synchronized with a selected received pulse.; Y v

9. A radio4 pulse position indicating system in'- cluding `meansi'or radiating synchronously dis crete `pulses ofradio energy from a plurality of predetermined locationsfremotely located receiving means including means for receiving saidv pulses, asource of local oscillations.r a timing indicator, means connecting said source to said 1ndicatorl indicator at a ,substantiallyconstant rate, means connecting said receiverand local source for synchronizing said localA oscillations andsaid pulses. and means for applying said received pulses to said indicator to indicate the of said pulse'reception thereby to indicate the difference in the .distances between each of said lol cations and said remotely located receiving means.

10. A radio4 pulse position indicating system in-` cluding means for radiating pulses of radio energy from a. plurality of predetermined locations, the radiation of said pulses so that all pulses are radiated in predetermined phase relation, remotely located receiving means including means for receiving said pulses, a timing indicator,'a source of oscillations, means for adjusting the frequency of said oscillations, means connecting said source to said indicator for driving said indicator at a. substantially constant rate, and means connecting said receiving means to said indicator for applying received pulses to said indicator to denote the relative times of reception of said pulses whereby the diiference in the distances between said locations and said remotely located receiving means may be' for applying said oscillations to drive said diilererces in times l 

